This invention relates to a system for monitoring and controlling strip material movement. More particularly, the invention relates to a system for monitoring and controlling strip material to be drawn through one or more work stations at a constant rate. Operations involving, for example, the working of steel strip material often require that the material move through the work stations at a constant and/or controlled rate unaffected by variations in the unspoiling rate. In operations involving the continuous coating of metal strip material, for example, the strip may be run through the coating stations at speeds of 600 feet per minute or more. The uncoated metal is usually supplied from rolls; at relatively frequent intervals, the leading edge of a new roll of uncoated metal must be welded to the trailing end of the preceding roll. This is accomplished by stopping the feed movement long enough to weld the trailing end of the preceding roll end to the leading end of the suceeding strip. After welding is completed, the strip resumes forward movement to feed from the new supply reel.
A depending loop is formed in the strip material at one or more locations along the path of strip movement to provide a temporary reservoir of strip. As is well known to those skilled in the art, the depending loop acts as a pool or reservoir from which strip can be drawn when the supply is temporarily stopped. As is apparent, it is necessary to provide means for monitoring the loop so that the system operator can gauge the amount of time the supply feed can be stopped. In addition, loop monitor systems provide an indication of problems occurring in movement of the strip through the system.
One known type of loop monitor/control system utilizes a photocell arrangement to detect the amount of strip in the loop. Photocell loop control systems are shown in U.S. Pat. No. 2,448,823 issued Sept. 7, 1948 to F. K. Schefe; U.S. Pat. No. 2,907,565 issued Oct. 6, 1959 to J. D. Sauter; U.S. Pat. No. 3,236,429 issued Feb. 22, 1966 to S. Klein; U.S. Pat. No. 3,240,411 issued Mar. 15, 1966 to S. A. Zarleng.
The present invention provides a loop monitor and control system using photocell detectors. The invention incorporates certain new and advantageous features not found in the prior art. The photo-electrical digital loop monitor and control system of this invention provides remote indication of loop position. The system has inherent balance, linearity and gain, which eliminate the need for gain or photocell adjustment rheostats. In addition, the system is essentially immune to noise, uses standard reliable solid state components, is simple to understand, test and repair, and requires no active components in the scanner.